1. Field of the Invention
The invention pertains to the field of self-sustained oscillators, and more particularly to oscillators of high reliability being capable of sustaining oscillations after a component failure.
2. Description of the Prior Art
An oscillator is an amplifier with feedback circuitry which provides 360 degrees of phase shift to the output signal and couples the phase-shifted signal to the input port of the amplifier. When this circuit provides sufficient regenerative feedback the amplifier becomes unstable and begins to oscillate at a frequency determined by the resonant characteristics of the feedback circuit. Should an element in this feedback circuit fail, the oscillator fails. To maintain the desired oscillator output signal after a component failure the prior art utilizes multiple phase locked loops to control the oscillations. Should one or more loops fail, the output characteristics of the oscillator are maintained by the remaining operating phase locked loops. This technique requires extensive circuitry, occupies an appreciable area on a circuit board, consumes an appreciable amount of power, and is expensive to implement.
Since oscillator failure is caused by the breakdown of a component in the oscillator circuit, a desired level of reliability may be achieved by providing failure compensation only for those components in the circuit having relatively high failure rates. This greatly reduces the complexity, size, and cost of an oscillator circuit for a desired level of reliability.